This invention relates to the manufacture of nonwoven fabrics from polytrimethylene terephthalate (PTT) based staple fibers. More specifically, the present invention relates to a process for producing such nonwovens which involves forming the web by carding the PTT fibers and then mechanically binding them by hydroentanglement.
As described in the 1987 Encyclopedia of Polymer Science and Engineering, Volume 10, page 204+, nonwoven fabrics are porous, textile-like materials, usually in flat sheet form, which are composed primarily or entirely of fibers assembled in webs. Nonwoven fabrics are manufactured by processes other than spinning, weaving, or knitting. The ASTM definition of nonwoven fabrics is xe2x80x9ca structure produced by bonding or the interlocking of fibers, or both, accomplished by mechanical, chemical, thermal, or solvent means and the combination thereof.xe2x80x9d The biggest advantage of nonwoven fabrics is their cost to manufacture and that they are usually made directly from raw materials in a continuous production line which allows the manufacturer to eliminate a number of conventional textile operations.
Thin woven webs can be formed of most natural fibers, including wood pulp, cotton, and manila hemp. Rayon and cellulose acetate are also used. Presently, synthetic fibers including polyethylene terephthalate, nylon-6, nylon-6,6, polypropylene, and polyvinyl alcohol fibers are used in commercial nonwoven fabric manufacture.
Staple fibers are used as the raw material for the manufacture of nonwoven fabric webs. Staple fibers are fibers which are long enough to be used in conventional spinning equipment. Generally, the fibers are between 1.2 and 20 centimeters long, but some fibers may be longer than that. Dry processing methods, such as carding and air-laying, are used in the formation of the nonwoven web.
In carding, the webs are produced using conventional textile carding machines. Bales of staple fiber are opened by machines equipped with sharp teeth or needles to tear the fibers. This process is called picking. Clumps of staple fibers from the picking process are first separated mechanically into individual fibers and then formed into a coherent web in the carding machine which utilizes opposed moving beds of closely spaced needles to pull and tease the clumps apart. There is a large rotating metal cylinder covered with card clothing (comprised of needles, wires, or fine metallic teeth embedded in a heavy cloth or a metal foundation) at the center of the machine. The moving beds of needles are wrapped on or around the cylinder and narrow metallic flaps which are held on an endless belt moving over the top of the cylinder. The cylinder moves faster than the flats and the clumps between the two beds of needles are separated into individual fibers which are then aligned in the machine direction as each fiber is held at each end by individual needles from the two beds. The fibers engage each other randomly and form a coherent web.
After the web is formed, the fibers must be bonded in order to form a web with sufficient strength. Bonding can be carried out by both adhesive and mechanical means. Types of adhesive bonding include latex bonding, print bonding, spray bonding, foam bonding, and thermal bonding. Mechanical bonding utilizes frictional forces between the fibers and methods include hydro entanglement (spun lace, water punch), needle punching, and stitch bonding.
In the hydroentanglement process, high pressure water jets entangle the fibers. Usually, a staple fiber web is made on a perforated belt and is passed under high pressure water jets. The high pressure jets of water cause the fibers to migrate and entangle including to the perforation in the belt. The belt is then impregnated with binder in order to seal segments of the structure. U.S. Pat. No. 3,485,706 describes a hydroentanglement process for making nonwoven webs. This patent is herein incorporated by reference for the purpose of adding to the description of the present invention.
Japanese Public Patent Application JP 11089869A describes a composite structure having air permeability which is formed by laminating a thermoplastic synthetic resin film onto a nonwoven fabric consisting of PTT fiber. PTT was used because the final product was softer and better in elasticity than polypropylene, polyethylene terephthalate (PET), or polyamides (PA or nylon). The recommended method for making the nonwoven fabric is spun bonding, in which fibers and web are made simultaneously directly from the bulk polymer. The bulk polymer is melted, extruded, and drawn to filaments that are randomized and deposited onto belts as a continuous virtually endless web. The melted polymer is forced through very fine holes in a special die into a high velocity air stream wherein the polymer is formed to very fine, although irregular, filaments of indeterminate lengths. The reference generally states that other methods, such as carding, can be used to make the web and that the web can be further treated by other methods, including hydroentanglement, although no details are provided.
This invention relates to making high quality, soft and relatively elastic nonwoven fiber webs from polytrimethylene terephthalate (PTT). Staple PTT fibers are first manufactured. Usually, this involves spinning the polymer into fibers and then cutting them to a length of from 10 to 200 millimeters, preferably 25 to 80 mm, and a fiber weight of 0.1 to 20, preferably 0.5 to 10, deniers per filament;. Thereafter, the fibers are carded and hydroentangled. This combination of steps produces high quality PTT nonwoven fabrics, i.e., which are softer than fabrics from other materials, require less energy to hydroentangle, can be manufactured at higher carding rates, and have a higher dye yield.
The PTT staple fibers are first carded. This can be carried out in conventional carding machines wherein the web is crosslapped at a belt speed of up to 1000, preferably 10 to 1000, most preferably 100 to 300, meters per minute, a cross lap of wet of 1 to 50 layers, preferably 3 to 10, and a web weight of 5 to 500 g/m2, preferably 10 to 100, in a carding machine selected from the group consisting of roller-top, flat-top, and layering types. The web is mechanically bonded the web by hydroentanglement at a belt speed of up to 500 meters per minute, preferably 5 to 500, most preferably 50 to 200, with from 1 to 10 multiple passes and a water jet hydraulic pressure of 1 bar to 500 bar (100 to 50000 kPa). Our process requirements for the carding are: Carding at 3 meters/minutes to give a target web weight of 50 g/m2 with 8 layers of crosslapping.
Hydroentanglement can be carried out in conventional textile hydroentanglement apparatus including water jet injection, dewatering or vacuum boxes, a filtration, a water removing system, a perforating unit, drying, and winding. Special apparatus and process conditions for the hydroentanglement of PTT include lower water jet pressure needed than the normally used for PET and nylons.